1. Field of the Invention
The invention relates generally to the production of ink and paper pigments and fillers and more specifically to the production of under four micron sized particles of potassium aluminum sulphate to substitute for relatively more expensive titanium dioxide.
2. Description of the Prior Art
Titanium dioxide is principally used as a pigment to provide brightness, whiteness and opacity for paints and coatings, plastics, paper, inks, fibers, food and cosmetics. Titanium dioxide is by far the most widely used white pigment in the world, only diamonds have a refractive index higher than titanium dioxide. A high refractive index translates to high opacity. Only magnesium oxide is whiter than titanium dioxide, but the refractive index of this material is much lower. So much more magnesium oxide would be needed in a paint for the same opacity. For practical purposes, titanium dioxide is preferred.
Nature does not provide titanium dioxide in a form that is directly usable, it is usually associated with iron, either as ilmenite or leuxocene ores. Titanium dioxide is also mined in one of its purest forms, as rutile beach sand. The most important deposits in the world include rutile (beach sand) and ilmenite soaps, and these ores are the principle raw materials used in the manufacture of titanium dioxide pigment.
In 1995, titanium dioxide pigment, valued at about $2.6 billion, was produced by five companies at eleven plants in nine American states. In 1995, about forty-seven percent of titanium dioxide production was used in paint, varnishes, and lacquers; about twenty-four percent was used in paper; about eighteen percent in plastics; and eleven percent went to miscellaneous uses such as catalysts, ceramics, coated fabrics and textiles, floor coverings, printing ink, roofing granules, etc.
The production of titanium dioxide pigments is a two step process. The first step is to purify the ore, and is basically a refinement step. This may be achieved by either the sulfate process, which uses sulfuric acid as a liberating agent, or the chloride process, which uses chlorine as the liberating agent. Once refined, and developed to the appropriate particle size, the pigment may be surface treated with inorganic oxides or an organic material to give each grade its unique characteristics.
The sulfate process for producing titanium dioxide pigments is often referred to as the older process, relative to the more modern chloride process. The sulfate process is used to produce high quality titanium dioxide pigment grades for the ink, fibers and paper industries. Kronos, Inc. (Houston, Tex.), for example, was granted patents for the sulfate process and has been producing titanium dioxide pigment using this process continuously since 1916. Since the late 1970's, Kronos has also manufactured grades using the chloride process. The chloride process was developed by the Kronos research and development group in Leverkusen, Germany, and commissioned its first chloride plant in the late 1970's.
A high purity rutile titanium dioxide is used in electroceramics for its dielectric properties, in vitreous enamels for its ease of fusion, in glasses to modify the refractive index and to improve the thermal and mechanical properties, in containers to absorb ultraviolet light for food preservation, in ceramics to enhance sintering and improve the thermal and chemical resistance, and in arc welding to ensure excellent ionization and easy re-ignition of the electrode to prevent electrode sputtering and control slag fluidity.
The rutile titanium dioxide grade is typically produced via the sulfate process, with low abrasion and high gloss. High brightness and very good opacity allows for this to be an ideal pigment for ink formulations, particularly rotogravure and polyamide flexo inks where it combines excellent dispersion, high gloss and opacity with very low abrasion.
Titanium dioxide pigments can be designed for ease of dispersion in many aqueous applications with minimal requirement for dispersing agents. Such pigment can be added at the beater or hydropulper to improve the opacity and brightness of the finished sheet. It can be used in the dry state as received, or can be slurried in water at the mill site to take advantage of slurry additions. It is also used to enhance opacity and brightness of paper coatings. It disperses readily in water at high solids without additional dispersing agent over that normally used in the coating mixture. The pigment can be used for white sidewall rubber goods that provide self-cleanup through chalking and resistance to ozone cracking. Its low abrasion properties promote its application in rubber thread compounds, both extruded and cut rubber thread. Cost effectiveness may be obtained in white plastic film, sheeting and profiles. Titanium dioxide pigment is used in traffic marking paints where an anatase grade is permitted. Field tests of traffic stripes indicate that the weathering of pigmented traffic stripes result in improved night visibility with minimal film loss. Titanium dioxide pigment may be used in white exterior aqueous and non-aqueous paints to impart controlled chalking.
Titanium dioxide pigment can be used in melamine laminate compositions where its resistance to ultraviolet light discoloration is outstanding. Titanium dioxide pigment can provide high brightness and very high resistance to ultra-violet discoloration in pigmented decorative papers for melamine formaldehyde laminates. KRONOS 2081 pigment is suitable for use in printing inks which are used in melamine-formaldehyde laminate systems. KRONOS 2081 pigment is suitable for pigmentation of melamine formaldehyde resins.